Test: Cellular Development - 1 - MCAT MCQ

The fact that the cell type can self-renew indicates its stem cell nature. However, its ability to differentiate into only one cell type suggests that it is unipotent, meaning it has a limited potential for differentiation into specific cell types. In this case, it can differentiate into only one specific cell type. Since the cell type is discovered in the central nervous system of mice, it is referred to as a somatic stem cell, as it is not derived from embryonic tissues.

The daughter cells produced per differentiation event in the population undergoing stochastic differentiation would be twice that of the population undergoing obligate asymmetric replication, then Option A would be the correct answer.

In this case, the population undergoing stochastic differentiation would produce two daughter cells per differentiation event, while the population undergoing obligate asymmetric replication would produce only one daughter cell per differentiation event. This indicates that the rate of daughter cell production is higher in the former group compared to the latter group.

Immunohistochemistry is a commonly used technique that utilizes antibodies to detect and visualize specific proteins or glycoproteins within tissue samples. In this case, the researchers can use immunohistochemistry to examine the expression levels and localization of the molecules responsible for cell-cell communication in both embryonic and adult monitor lizards. By comparing the staining patterns and intensities between the two stages, they can directly confirm any downregulation or difference in the expression of these molecules in adolescents and adults compared to the embryonic stage.

The mitochondrion is known to have a significant role in apoptosis. It is involved in the intrinsic pathway of apoptosis, which is activated by various stimuli such as DNA damage or cellular stress. During apoptosis, mitochondria release proteins, such as cytochrome c, into the cytoplasm, which triggers a cascade of events leading to cell death. These released proteins activate caspases, enzymes responsible for dismantling the cell and executing the apoptotic process. The mitochondrion is also involved in regulating the balance between pro-apoptotic and anti-apoptotic proteins, influencing the cell's fate in terms of survival or death.

During apoptosis, cytochrome c is released from the mitochondria into the cytoplasm. This release is a key step in the activation of the apoptotic pathway. By detecting increases in cytoplasmic concentrations of cytochrome c, researchers can monitor the progression of apoptosis in real time. Various techniques, such as fluorescence microscopy or flow cytometry, can be employed to detect and quantify cytochrome c levels in the cytoplasm of live cells.

Measuring decreases in mitochondrial volume (Option B) or increases in mitochondrial concentrations of cytochrome c (Option C) are not typically used as direct indicators of apoptosis progression. Changes in mitochondrial volume or cytochrome c levels may occur during apoptosis, but they may not be as reliable or direct measures of apoptosis progression as the changes occurring in the cytoplasm.

Measuring increases in cytoplasmic volume (Option D) may not be a specific indicator of apoptosis since changes in cell volume can be influenced by various cellular processes unrelated to apoptosis.

Caspases are a family of proteases (enzymes that cleave proteins) that play a central role in the execution of apoptosis. During apoptosis, caspases are activated and cleave various cellular proteins to initiate and propagate the apoptotic process. Caspases specifically recognize and cleave peptide bonds after aspartate residues within their target proteins. This cleavage of aspartate residues leads to the breakdown of critical cellular components and ultimately results in the characteristic changes associated with apoptosis.

Which of the following is not a mechanism for induction of cell differentiation?
A.Direct contact
B.Paracrine signalling
C.Formation of gap junctions
D.Autocrine signalling

The Hayflick limit refers to the finite number of times cells can divide before undergoing senescence or cell death. One factor that contributes to this limit is the gradual shortening of telomeres, the protective caps at the ends of chromosomes. As cells divide, their telomeres progressively shorten, eventually leading to cellular senescence.

To extend the Hayflick limit, researchers would likely focus on finding ways to counteract telomere shortening or maintain telomere length. One possible approach is to investigate methods to extend the length of telomeres, either by activating telomerase, the enzyme responsible for telomere maintenance, or by exploring other mechanisms to prevent or slow down telomere shortening. By preserving or lengthening telomeres, the cells would have an increased capacity for division before reaching senescence.

Eliminating telomeres altogether (Option A) or shrinking the length of telomeres (Option B) would not be desirable approaches, as telomeres serve crucial protective functions and their complete elimination or further shortening could lead to genomic instability and other detrimental effects.

Downregulating the production of telomerase (Option C) could also be a potential avenue of investigation to limit cell division and prevent excessive proliferation in certain contexts, such as cancer. However, in the case of extending the Hayflick limit, the focus would be on maintaining or extending telomere length rather than inhibiting telomerase production.

While skin cells (Option A), brush border cells (Option B), and pluripotent stem cells (Option D) can undergo replicative senescence, cardiac muscle cells (Option C) have a limited ability to regenerate and do not typically undergo replicative senescence. Cardiac muscle cells have a very low rate of cell division and possess a limited capacity for self-renewal. Therefore, they do not enter replicative senescence but instead can undergo other forms of age-related cellular dysfunction.

In motile macrophages, compared to stationary macrophages, one would not expect to find increased levels of DNA polymerase activity. DNA polymerase is primarily involved in DNA replication, which is not directly associated with cell movement.

The cytoskeletal model of cell movement focuses on the rearrangement of cytoskeletal components, such as actin filaments and microtubules, to drive cell motility. These changes involve processes like actin polymerization, formation of lamellipodia and filopodia, and cytoskeletal contractility.

While increased levels of mRNA (Option A), ribosome activity (Option C), and gene transcription (Option D) may be associated with the increased protein synthesis required for cell movement, they are not specifically related to the cytoskeletal model of cell movement. These processes are part of the general cellular machinery involved in protein synthesis and gene expression.